The proteolytic enzyme renin, which has a molecular weight of about 40,000, is produced in and secreted into the blood by the kidney. It is known to be active in vivo in cleaving the naturally-occurring plasma glycoprotein angiotensinogen, in the case of human angiotensinogen at the bond between the leucine (10th) and valine (11th) amino acid residues at the N-terminal end of the angiotensinogen: ##STR1## The circulating N-terminal decapeptide (angiotensin I) formed by the above cleaving action of renin is subsequently broken down by the body to an octapeptide known as angiotensin II. Angiotensin II is known to be a potent pressor substance, i.e. a substance that is capable of inducing a significant increase in blood pressure, and is believed to act by causing the constriction of blood vessels and the release of the sodium-retaining hormone aldosterone from the adrenal gland. Thus, the renin-angiotensinogen system has been implicated as a causative factor in certain forms of hypertension.
One means of alleviating the adverse effects of the functioning of the renin-angiotensinogen system is the administration of a substance capable of inhibiting the angiotensinogen-cleaving action of renin. A number of such substances are known, including antirenin antibodies, pepstatin and naturally-occurring phospholipid compounds. European patent application No. 45,665 (published Feb. 2, 1982) discloses a series of renin-inhibiting polypeptide derivatives of the formula EQU X-Y-Pro-Phe-His-A-B-Z-W
in which X may be hydrogen or an amino-protecting group, Y may be absent, B is a lipophilic amino acid residue, Z is an aromatic amino acid residue, W may be hydroxyl and A may be, inter alia, ##STR2## with each of R.sup.1 and R.sup.2 being a lipophilic or aromatic side chain. According to the definitions set forth in this published patent application, it is not contemplated that either A or Z could be statine or that B could be lysine.
European Patent Application No. 77,028 (published Apr. 20, 1983) discloses a series of renin-inhibiting polypeptide compounds having a non-terminal statine or statine derivative residue. Included within this series are compounds having a phenylanine-histidine-statine sequence. However, this published patent application does not disclose the placement of lysine immediately after the -Phe-His-Sta- sequence.